1. Field of the Invention
This invention relates to an automatic document feeding device capable of automatically feeding documents stacked on a document tray one by one to a document setting portion defined on a platen in a copying machine and sending back the document after copying from the document setting portion to the document tray, so as to repeat the copying operation for each document. More particularly, this invention relates to a recirculation-type document feeding device having a function of alternatively feeding the copied document from the document setting portion to a document discharge tray or the document tray.
2. Description of the Prior Art
Not infrequently there are cases that a plurality of original documents are repeatedly fed several times one by one to a document setting portion of a copying machine to be copied, consequently obtaining copied matters for binding books. At that time, it may be advantageous to consecutively make copies of the given documents by one volume in order to facilitate page numbering of the copied matters. To automatically repeat the copying operation for the original documents volume by volume, the copied documents are required to be sent back to a document tray on which the documents are initially stacked.
Automatic document feeding devices of this type have been so far proposed by Japanese Patent Application Public Disclosures Nos. SHO 60(1985)-113225, HEI 1(1989)-231739 and HEI 1(1989)-288542, U.S. Pat. No. 4,234,180 (corresp. to Japanese Pat. Appln. Pub. Discl. No. SHO 56(1981)-6263), and U.S. Pat. No. 4,699,365.
The conventional document feeding devices noted above are all adapted to repeat simplex copying operation for copying a plurality of original documents each having an image to be copied on one side. In these conventional devices, original documents are stacked on a document tray and automatically fed one by one from the document stack on the document tray to a document setting portion on a platen while drawing out the lowermost document from the document stack. The original document in the document setting portion after copying is merely sent back to and put on the stack of original documents which are not yet copied (uncopied documents). A mechanism for separating the copied documents returning to the document tray and the uncopied documents remaining on the document tray has been formerly proposed by Japanese Patent Appln. Public Disclosure No. SHO 60(1985)-48854. This mechanism has a function of counting the documents sent back to the document tray to decide completion of copying the required number of documents.
In any conventional document feeding device, after copying the required number of documents, the documents are all sent back to the document tray. This means that it would be next to impossible to take out even one copied document from the stacked documents on the document tray until completing the copying for all the given documents, because the decision as to whether, for example, the first document has been copied required times is difficult.
In a case that many documents are required to be copied during a busy time, there has been often felt a disadvantage such that any document cannot be taken out from the stacked documents on the document tray until completing the copying of all the documents required times. Thus, there has been a need for a document feeding device capable of discriminating the copied documents from the documents stacked on the document tray and taking out only the copied documents during copying as occasion demands. Besides, the documents sent back to the document tray after copying are required to be taken out in the initial order of page. A document feeding device having a function of fulfilling these requirements would be complicated in structure and increased in size.
Of the document feeding device of the type such that original documents to be copied can be automatically recirculated, there has conventionally been no device capable of duplex copying. That is, it has been impossible to repeatedly copy a plurality of documents each having images on both sides to obtain a plurality of volumes of copied matters arranged properly in order of page.
Furthermore, generally in the conventional copying machine, an optical scanning system disposed under a transparent platen for reading the image on the document is moved across the entire surface of the platen in any case. Namely, it is not rational that, even when the given document is small in size, the entire area of the platen is optically scanned for reading the image like a document of large size is copied. The copying speed would be increased if only the document reading area defined on the platen is scanned in accordance with the size of the given document.